Selective color modification

ABSTRACT

An apparatus and method .Iadd.is described .Iaddend.for the modification of the color of television pictures in arbitrarily selected regions of the color space and of the picture. A region within which color modification is to take place is defined by establishing the bounds, or limits, for the region. Apparatus is described by which a determination can be made whether any given picture element lies within the region. For those picture elements which lie within the region, modification voltages are added to the television signals to accomplish the desired color modifications. Display apparatus is described which facilitates setting of proper bounds for the color modification region.

FIELD OF THE INVENTION

This invention relates to the reproduction of color pictures byelectronic means such as are utilized in television and in scanners usedin making color separations for the printing industry.

DESCRIPTION OF THE PRIOR ART

In color television and in color printing, it is sometimes desirable toselectively modify certain chosen colors without affecting others.Heretofore, this capability has been provided by a non-linear matrixdevice invented by Monahan et al, U.S. Pat. No. 3,558,806. The Monahaninvention has been implemented and made available to the industry by theRCA Corporation in a device known as the Chromacomp and also by thePhilips Audio Video Systems Corporation in a device known as theVariable Matrix. These devices permitted independent adjustment of thehue and saturation for each of the six primary and secondary hues: red,cyan, green, yellow, blue and magenta. In other words, the chrominanceplane is divided into six sectors, each centered on the aforesaid hues;within each sector, the hue and saturation of the colors lying withinthat sector can be altered without affecting color lying outside thatsector. With the non-linear matrix device invented by Monahan it is notpossible to change the color of one object whose color lies within onesegment of the chrominance plane without affecting the color of otherobjects in that segment. Moreover, because the color of a given objectusually is represented by an area in the chrominance plane and not justa single point, and because that area may lie in two or more adjacentsegments, adjustment of the color of that object may require coordinatedadjustments in the adjacent segments. While this can be done, itpresents some difficulty to the colorist operating the equipment.

SUMMARY OF THE INVENTION

This invention provides a capability for modification of both theluminance and chrominance of the colors in an arbitrarily selectedregion of the color space while not affecting the colors outside thatregion; the selected color space region may further be delimited to anarbitrarily selected region of the picture itself. This modificationcapability can be applied independently in a multiplicity of regions.

In order to guide the colorist in his choice for the location, shape andsize for any of the color modification regions, this invention providesseveral cathode ray tube displays. In one of these displays the monitorscope, which normally displays either the original picture or themodified version, can be blanked out except in the region selected formodification. In another of these displays the monitor scope, or itsequivalent, shows the area in the chrominance plane of the colormodification region. In still another of these displays the monitorscope, or its equivalent, shows the extent along the luminance axis ofthe color modification region.

In the television industry there is a particular need for colormodification of picture material which is stored on color film.Typically, this material is a composite of a number of scenes, eachscene requiring independent modification. Because of the rapidity withwhich one scene changes to the next, scene-by-scene instructions forcolor modification are stored in a digital computer and appliedautomatically as the scenes change. This technology has been describedin U.S. Pat. Nos. 3,610,815, 3,637,920 and 4,096,523. This invention canalso be implemented in such computer controlled systems; when soimplemented, some of the functions which would otherwise be implementedin apparatus can be handled by computer software.

In color television systems, the color signals change too rapidly fordigital computer processing and storage; the digital computer is limitedto processing and storing control signals. However, color separationscanners for the printing industry can be implemented in such a way thatthe color signals pass through the computer and may be processed andstored in digital form. Such a digital computer-scanner has beendescribed in U.S. Pat. No. 3,612,753. This invention can be implementedin such systems, where the color signals are in digital form andaccessible to a digital computer; when so implemented, many of thefunctions which would otherwise .[.by.]. .Iadd.be .Iaddend.implementedin apparatus can be handled by computer software.

BRIEF DESCRIPTION OF THE DRAWINGS

This invention is described in greater detail by reference to theFigures.

FIG. I depicts the chrominance plane.

FIG. II depicts .[.the basic.]. .Iadd.an .Iaddend.embodiment of thisinvention.

FIG. III depicts an embodiment of the control aspects of this inventionwhen used with a digital computer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In color television systems, three signals, Red, Green and Blue aregenerated by three camera tubes, each viewing the same picture butthrough red, green and blue filters respectively. In order to providecompatibility with monochrome reception and to facilitate transmission,the Red, Green and Blue signals are transformed into signals Y, I and Q.Upon reception the Y, I and Q signals are transformed back into Red,Green and Blue signals which are then used to excite the correspondingpicturetube phosphors. These transformations are referred to as"matrixing" and are well known to those skilled in the art.

The color of any picture element, thus, has three attributes, e.g., Red,Green.Iadd., .Iaddend.Blue or Y, I, Q, and may be thought of as beingrepresented by a point in a three dimensional color space. Thecoordinates in that space may be taken as Red, Green, Blue oralternatively as Y, I, Q. Matrixing is equivalent to a change in thecoordinate system. The Y, I, Q coordinate system is of particularinterest because it corresponds with the human perception of color. Ycorresponds with the luminance or brightness of a color; the I and Qaxes lie in a plane of constant luminance. This plane is known as thechrominance plane and is depicted in FIG. I. Radial distance of thecolor point, 1, from the origin, 2, on this plane is known assaturation; angular position is known as hue. The angular positions ofthe primary and secondary hues, red, green, blue and cyan, magenta,yellow are shown on the periphery of FIG. I. The chrominance boundariesof a typical region selected for .Iadd.a specific .Iaddend.colormodification .Iadd.embodiment .Iaddend.are shown at UI, LI, UQ and LQ.The corresponding boundaries for the region along the luminance axis aredesignated as UY and LY but are not depicted in FIG. I.

The colorist, the person operating an equipment embodying thisinvention, selects the boundaries of the region within which he intendsto make a color modification by setting the bank of potentiometers, 3,shown in FIG. II. If the equipment permits further delimitation of theregion to a specified area of the picture by the inclusion ofpotentiometer bank, 4, and its associated comparators, 6, he would alsoset potentiometers, 4. This act of setting the potentiometersestablishes voltage levels which correspond with the region boundariesUI, LI, UQ, LQ, UY, LY, UH, LH, UV, LV, respectively.

The banks of comparators 5 and 6 determine whether the color signals Y,I, Q on the one hand, and whether the deflection signals H, V on theother hand, lie within the region selected. The comparators depictedhere are commercially available under the designation LM319. They havewhat is termed "open collector output", i.e., if the voltage at the +input 7 exceeds the voltage at the - input 8, the condition at theoutput 9 relative to the reference terminal 10 will be an open circuit;if the voltage at the + input 7 does not exceed the voltage at the -input 8, the condition at the output 9 relative to the referenceterminal 10 will be a short circuit. Thus, if, and only if, all threecolor signals lie within the boundaries of the selected region:

    UY<Y<LY and UQ<Q<LQ and UI<I<LI and UH<H<LH and UV<V<LV

where H is the signal voltage corresponding to the horizontal coordinateof a point in the picture .Iadd.and .Iaddend.

.[.where.]. V is the signal voltage corresponding to the verticalcoordinate of a point in the picture.Iadd., .Iaddend.

then the gate signal 11 will be at a level of plus six volts. If, on theother hand, any of the three color signals Q, I, Y, or any of the twocoordinate signals H, V, lie outside the boundaries of the selectedregion, one or another of the comparator output terminals 9 will be.[.short circuited.]. .Iadd.short-circuited .Iaddend.to the referenceterminal 10 and the gate signal 11 will be at a level of minus sixvolts. The electronic switches at 12 and 14, which are typified by thecommercially available unit designated as the CD4066A, will be in theclosed position shown when the respective control members 13 and 15 areat a potential of +6 volts; but they will be open when the controlmembers 13 and 15 are at a potential of -6 volts.

Control switches .[.19-26.]. .Iadd.19-25, .Iaddend.which can be operatedeither manually or remotely by means of relays, control the picture tobe displayed on the monitor scope 17 and to be available for recordingor transmission at 18. Table I lists the monitor scope pictures as afunction of the settings of control switches 19-25. Thus, for theunmodified picture to appear on the monitor scope 17, switches 23 and 24are put in the left position, switch 25 is put in the right position; asa result electronic switch 12 will be closed, electronic switch 14 willbe open, and the Q,I,Y signals alone will appear at the input to thesummation amplifiers 16 and upon the monitor scope 17.

For a modified picture to appear on the monitor scope 17 and to beavailable for transmission or recording at 18, the switches 19-25 areset in accordance with line 2 of Table I. If the color signals Q,I,Y orthe location V,H in the picture plane are outside the selectedmodification region, gate signal 11 will be at a potential of -6 volts,electronic switch 12 will be closed, electronic switch 14 will be open,.Iadd.and .Iaddend.only Q,I,Y will appear at the summation amplifiers 16and on monitor scope 17. On the other hand, if the color signals Q,I,Yand the location V,H in the picture plane are inside the selectedmodification region, gate signal 11 will be at a potential of +6 volts,both electronic switches 12 and 14 will be closed, the colormodification voltages MQ, MI, MY will be added to the unmodified colorsignals Q,I,Y in the summation amplifiers 16, and the modified colorwill appear on the monitor scope 17 and be available for recording ortransmission at 18. At this point the colorist can alter the colorwithin the modification region at will by adjusting the modificationpotentiometer bank 26.

                  TABLE I                                                         ______________________________________                                        Switch Positions                                                              Line 19    20    21  22  23  24  25  Monitor Scope Display                    ______________________________________                                        1    *     *     *   *   Lt  Lt  Rt  Unmodified picture                       2    Lt    Lt    Lt  Lt  Lt  Rt  Lt  Modified picture                         3    Lt    Lt    Lt  Lt  Lt  Rt  Lt  Picture blanked except in                                                     modification region                      4    Rt    Lt    Rt  Rt  Rt  Rt  Rt  Extent of modification                                                        region in chrominance plane              5    Rt    Rt    Lt  Rt  Rt  Rt  Rt  Extent of modification                                                        region along luminance axis              6    *     Rt    Rt  Lt  Rt  Rt  Rt  Extent of modification                                                        region in picture plane                  ______________________________________                                         * = either                                                                    Lt = Left                                                                     Rt = Right                                                               

The system depicted in FIG. II is based upon analog type comparators,switches and summation amplifiers. However, digital equivalents of theseelements are commonly available and can be used instead of their analogcounterparts. For example, SN74LS85 digital comparators can be used toprovide comparator action on digital signals; SN74LS157 data selectorscan be used as switches for digital signals; SN74LS83 binary adders canbe used to add digital signals. One or more of these digital typedevices could be used in place of the corresponding analog device ofFIG. II. If digital switching alone were to be employed usingSN74LS157s, the color modification signals would be supplied to it indigital form and the switch outputs would be converted to analog form bydigital-to-analog converters such as the DAC-08. If digital comparatorsand summation amplifiers such as the SN74LS85 and the SN74LS83 were tobe used in addition, the color video signals as well as the controlvoltages would be supplied in digital form. The MATV-0811 is an exampleof a state-of-the-art device for converting normal analog video voltagesinto digital form.

The system depicted in FIG. II is capable of modifying color in only oneselected region. By additional banks of potentiometers 3, 4, 26,additional banks of comparators 5, 6, additional electronic switches 12,14, and by appropriate channels in switches 19-25, a mulitiplicity ofregions can be established and independent color modifications made ineach region.

In addition, Red, Green, Blue instead of Q,I,Y signals may be operatedupon while correction and control can be exerted in terms of Q,I,Y. Thiscan be accomplished by the use of appropriate matrixing circuits totransform the voltage levels from potentiometer banks 3, 4, 26 into theRed, Green, Blue equivalents. Moreover, for convenience to the colorist,the upper and lower boundaries to a region may be obtained by theaddition and subtraction of voltages derived from controls specifyingwindow parameters; window parameters being the mean and difference ofthe upper and lower boundaries.

In the foregoing description relating to FIG. II, the color space regionand the picture plane region, which are described in terms of upper andlower boundaries for Q, I, Y, V and H, are a rectangular.[.parallelopiped.]. .Iadd.parallelepiped .Iaddend.in color space and arectangle in the picture plane. These particular shapes for the regionalboundaries result not only from the fact .[.tht.]. .Iadd.that.Iaddend.Q, I, Y, V and H are rectangular coordinate systems in theirrespective spaces but also from the particular circuitry chosen forillustration. Alternative shapes for the regional boundaries arepossible. For instance, a region in color space with ovoid boundariesand a region in the picture plane with oval boundaries could beimplemented with hardware or software no more .[.complicted.]..Iadd.complicated .Iaddend.to design or build than that required forregions with rectangular boundaries. The size and location of theseregions would still be defined by the same upper and lower boundariesfor Q, I, Y, V and H; these are now recognized to be values of thesecoordinates at the intersection of the regional boundaries with thecoordinate axes.

Some of these circuit elaborations may become inordinately extensive andthe large number of controls may become conducive to operating errors.In that case, a digital computer may be used advantageously to reducethe amount of circuitry and the number of controls. FIG. III illustrateshow control may be exerted by means of a digital computer; it depicts atypical control panel. Only one joystick control, 27, is employed. Thejoystick function is determined by which one of the control buttons28-34 is depressed; these functions are listed in Table II.

                  TABLE II                                                        ______________________________________                                        Button   Joystick Function                                                    ______________________________________                                        28       Move center of modification region .[.ih.]. .Iadd.in.Iaddend.                 chrominance plane                                                    29       Change dimensions of modification region in                                   chrominance plane                                                    30       Change center and extent of modification                                      region along luminance axis                                          31       Change center of modification region in                                       picture plane                                                        32       Change dimensions of modification region in                                   picture plane                                                        33       Change chrominance correction in                                              modification region                                                  34       Change luminance correction in modification                                   region                                                               ______________________________________                                    

At most, only one of the control buttons may be depressed at a giventime, the one depressed being indicated by backlighting. The joystick 27can be moved up or down, right or left. The up-down component of motioncontrols a multiple position switch; the right-left component of motioncontrols another multiple position switch. In operation, the joystick 27controls the rate and direction with which the computer is to change thefunction designated by the depressed control button. For instance, ifcontrol button 28 has been depressed, the position of joystick 27 willbe interpreted by the computer as an order to move the colormodification region in the chrominance plane; if joystick 27 is in itscenter position there will be no motion; if off center the colormodification region will move in the direction that the joystick 27 isdisplaced and at a rate proportional to the distance that the joystick27 is displaced from the center. The computer, by sensing the switchclosures actuated by the control buttons 28-34 and the joystick 27,makes all of the necessary computations to change the color modificationregion boundaries. Buttons 35-37 enable the colorist to select the colormodification channel by depressing the appropriate button momentarily.Button 35 resets the channel number to one; button 36 advances thechannel number by one; button 37 decreases the channel number by one.Buttons 38-40 enable the colorist to select the picture to be displayedon the monitor scope. Only one of these buttons may be depressed at agiven time, the one being depressed being indicated by backlighting.

Since the control panel described by reference to FIG. III operates, inthe main, by instituting changes, it is most desirable that the coloristbe given displays which depict the current situation. While this can beprovided largely by the monitor scope 17 as described earlier, it may bepreferable to confine the monitor scope to showing only the original,blanked and corrected pictures, and to provide another scope display asat 41 on FIG. III. Scope 41 shows the selected region on the chrominanceplane 42, the selected region along the luminance axis 43, the selectedregion on the picture plane 44, the number of the current channel 45,and the total numbers of channels in current use 46.

The computer software and hardware necessary to implement the functionsdescribed in connection with FIG. III are well known to those skilled inthe art of computer systems and need not be elaborated upon.

I claim:
 1. A color modification system for color television pictures,said pictures being represented by three color signals corresponding,respectively, to the three attributes of a color, wherein thereare:means for controlling three modification amounts, one for each ofthe three color signals, means for controlling upper and lowerboundaries for each of the three color signals, means for finding whenthe three color signals simultaneously lie within their respective upperand lower boundaries, and means for adding the three modificationamounts to each of the three color signals, respectively, only when thethree color signals are found to lie simultaneously within theirrespective upper and lower boundaries.
 2. The color modification systemof claim 1 wherein .[.the.]. said color attributes.[.and the.]..Iadd.,.Iaddend.said modification amounts and .[.the.]. said boundaries are allin terms of red.Iadd., .Iaddend.green and blue.
 3. The colormodification system of claim 1 wherein .[.the.]. said colorattributes.[.and the.]..Iadd., .Iaddend.said color modification amountsand .[.the.]. said boundaries are all in terms of luminance.Iadd.,.Iaddend.I and Q.
 4. The color modification system of claim 1 wherein.[.the.]. said color signals are red.Iadd., .Iaddend.green and blue, andwherein .[.the.]. said color modification amounts controlled and.[.the.]. said boundaries controlled are in terms of luminance.Iadd.,.Iaddend.I and Q, and wherein there are:means for calculating red.Iadd.,.Iaddend.green and blue modification amounts for addition to .[.the.].said color signals from .[.the.]. said color modification amountscontrolled in terms of luminance.Iadd., .Iaddend.I and Q, and means forcalculating red.Iadd., .Iaddend.green and blue upper and lowerboundaries for .[.the.]. said color signals from .[.the.]. said upperand lower boundaries controlled in terms of luminance.Iadd., .Iaddend.Iand Q.
 5. The color modification system of claim 1 wherein thoseportions of the picture to be modified are displayed byproviding.[.:.].means for blanking out all parts of the picture forwhich .[.the.]. said color signals do not all simultaneously lie withintheir respective boundaries.
 6. The color modification system of claim 1wherein .[.the.]. said upper and lower boundaries are provided by:meansfor calculating said upper and lower boundaries from window parameters,and means for controlling said window parameters, said window parametersbeing the mean and difference of .[.the.]. said upper and lowerboundaries.
 7. The color modification system of claim 1 wherein saidupper and lower boundaries and said modification amounts are controlledby .[.the.]. signals from a digital computer.
 8. The color modificationsystem of claim 7 wherein a sequence of television pictures represent amultiplicity of scenes in sequence and wherein there are.[.:.].means forchanging the boundaries and modification amounts at the start of eachscene.
 9. A color modification system for color television pictures,said pictures being represented by three color signals corresponding,respectively, to the three attributes of a color, and by two positionsignals corresponding to location in the picture plane, wherein thereare:means for controlling three modification amounts, one for each ofthe three color signals, means for controlling upper and lowerboundaries for each of the three color signals, means for controllingupper and lower boundaries for each of the two position signals, meansfor finding when the three color signals and the two position signalssimultaneously lie within their respective upper and lower boundaries,and means for adding the three modification amounts to each of the threecolor signals, respectively, only when the three color signals and thetwo position signals are found to lie simultaneously within theirrespective upper and lower boundaries.
 10. A method for colormodification of a scanned color picture, wherein there are three colorattributes for each picture element, comprising the steps of:selecting acolor space region by setting upper and lower boundaries for each of thethree color attributes, and adding modifications to .[.the.]. said threecolor attributes of each of .[.the.]. said picture elements only forthose of .[.the.]. said picture elements whose color attributes all liewithin .[.the.]. said color space region.
 11. A method as described inclaim 10 wherein the final selection of the color space region isfacilitated by viewing said color picture with all of said pictureelements not lying within .[.the.]. said color space region blanked out.12. A method as described in claim 10 wherein the final selection of.[.the.]. said color space region is facilitated by.[.:.].viewing achrominance plane plot and a luminance plot of .[.the.]. said picture,said plots displaying the location of .[.the.]. said color space region.13. A method as described in claim 10 wherein for .Iadd.each.Iaddend.picture element there are two location attributes describingthe location of .[.the.]. said picture element in the picture plane, andwherein:a picture region is also selected by setting the upper and lowerbounds for each of .[.the.]. said two location attributes, and .[.the.].said modifications are added to .[.the.]. said three color attributesonly for those picture elements for which .[.the.]. said locationattributes lie within .[.the.]. said picture region.
 14. A method asdescribed in claim 13 wherein the final selection of said picture regionand said color space region is facilitated by viewing chrominance plane,luminance and picture plane plots of .[.the.]. said picture, said plotsdisplaying the location of .[.the.]. said regions. .Iadd.
 15. A systemfor modifying the color representation of an object in a color picturecomprising:means for defining a region in a color space, the color spacebeing defined by color coordinates and the region including the colorrepresentation of the object, the color representation having colorcomponents with each color component being a value along the respectivecolor coordinate; and means for modifying the color representation ofthe object within the region to produce a new color representation forthe object. .Iaddend. .Iadd.16. A system as recited in claim 15 furthercomprising means for delimiting on a display the object, the colorrepresentation of which is within the region. .Iaddend. .Iadd.17. Asystem as recited in claim 15 further comprising means for defining awindow within the color picture encompassing the object so that only thecolor representation for the object is affected by the modifying means..Iaddend. .Iadd.18. A system as recited in claim 17 further comprisingmeans for delimiting on a display the object within the window, thecolor representation of which is within the region. .Iaddend. .Iadd.19.A system as recited in claim 18 wherein the region defining meanscomprises means for establishing boundaries with respect to each colorcoordinate. .Iaddend. .Iadd.20. A system as recited in claim 19 whereinthe modifying means comprises: means for determining when all colorcomponents of the color representation of the object lie within therespective boundaries; and means for combining a selectable modificationamount for each color component of the color representation when allcolor components of the color representation lie within the region toproduce the new color representation for the object. .Iaddend.